Adjustable mounting



4 Sheets-Sheet 1 l; L. STEPHAN ADJUsTgu MOUNTING Filed'Ma'y 51, 194e 2.41555 2, w Z. V./ X5 v ApJ/ww? @7% July 22, 1947. y

l. L. STEPHAN July 22,1947.v 2,424,513 ADJusTlApi-E MOUNTING l I i Filed May 31, 1946 4 Sheets-Sheet 2 f INVENTOR /NGO L. 57E/@HHN July 22, 194-7.

l. L. STEPHAN ADJUS TABLE MJQUN'TING Filed Mayil, 194e 4 Sheets-Sheet 3 Patented i July 22, 1947 vADJUSTABLE MoUNTI-NG Ingo L. Stephan, Delanco, N. J., assignor to Philco Corporation, Philadelphia, Pa., a cor poration of Pennsylvania f Application May 31,

' j 15 Claims.

l The invention hereinafter described and claimed relates to projection type image-forming optical systems and is especially concerned with apparatus adapted to adjustably support l. l

5 To the foregoing general ends, the invention cathode-ray tubes used in projection television receivers.

In such receivers, aswell as certain other projection apparatus to which the concepts of the invention are applicable, it is necessary to effect precisely controlled relative movement .between the cathode-ray tube (or other device upon which a primary image exists) and certain optical elements which define an optical axis. Such movement is required in the achievement of proper Y igocus upon a viewing surface or screen. v

It has been recognized that the more desirable way to accomplish such focusing is to move the cathode-ray tube, rather than moving one or more of the optical elements, but, heretofore, no

apparatus has been available by means of which suchfocusing movements could be both readily and accurately effected. Universal-type tube mountings have been utilized heretofore, but these have been unstable during adjustment, and have been almost inaccessible.

While the present invention is of broader applicability, it is particularly useful in projection television receivers utilizing a Schmidttype reflective optical system, that is, receivers which include a mirror and a correcting plate between which is arranged a cathode-ray tube, said mirror and plate dening an optical axis. A television receiver of this general type, to which the invention is particularly applicable, is'disclosed and claimed in the copending application of Ernest H.Tra'ub, Serial No. 649,359, iiled February 21, 1946, and assigned to the assignee of the present invention. For purposes of illustration, the accompanying drawings and the following description are directed to exposition of the invention as embodied in such a television receiver.

It is a primary object of the present invention to provide a mounting for cathode-ray tubes-or other devices having a primary image screenby the use of which mounting said tubes may be readily and precisely oriented with respect to an optical axis, whereby to accomplish necessary focus adjustments.

More particularly, the invention has as an object the provision of Schmidt-type projection apparatus, including a cathode-ray tube enclosed within a dust resistant housing, in which apparatus the tube screen may be given any threedimensional angular adjustment, within'qjefined limits, all adjustment movements taking place y(o1. 25o-141) 1946, Serial No. 673,337

about a predetermined point lying substantially in the plane of the tube screen, and in which all vadjustments may be made from points exterior to the housing.

provides apparatus for rotationally adjustingthe tube, preferably about the geometrical center of the tube screen, whereby properly to orient said l screen with respect to an optical axis, said appal ratus comprising: a movable frame member carrying said tube and mounted for rotation about s a pair of rotational axes passing through said point in substantially right-angularly related directions, means normally restraining said frame l5 against rotation about said axes and being releasable to provide for rotation of the frameand consequent adjustment of said tube-about either axis selectively, and means effective to produce rotation about the axis selected. A third axis, the longitudinal axis of the tube, is generally perpendicular to both the tube screen and the pair of axes aforesaid, and also passes through the geometrical center of the tube screen or other predetermined point selected. Axial movement of the tube may be effected along this axes are individually defined and the above-mentioned restraining means prevents loss of adjustment about one axis, while adjustment .isbleing made about the other.

It is also an object of the present invention to provide apparatus in accordance with the fore- ,-going, in which the focus adjustments may be readily and accurately made in the field, the simplicity of the adjustment operations being such as to obviate the necessity for highly skilledhandling. f

The invention further contemplates certain novel constructional features and arrangements hereinafter described and illustrated in the attached drawings, in which:

Figure l is a somewhat diagrammatic vertical sectional view illustrating a television receiver constructed in accordance with the copending application above-identified and embodying the apparatus of the present invention;

Figure 2 is a view in perspective, on a larger the manner in which the tube is adjusted about the several axes referred to above;

Figure 4 is a rear elevational View of the a-pparatus illustrated in Figure 2; and

Figure 5 is a sectional View taken along the line 5 5 of Figure 4.

Referring rst to Figure 1, there is shown a picture projection system for television receivers constructed in accordance with the above-identiiied copending application, the parts of which receiver are housed within a cabinet shown in general outline at I0, and having a lid II hinged to the cabinet along the rear Wall thereof, as indicated at l2. The projection system includes a cathode-ray picture tube I3 having a fluorescent screen or target area in the forward face thereof, a spherical mirror I4, an-aspherically configured correction plate I5, a plane reflector i6 supported upon the upper inside surface or" the front portion of the cabinet, and a Viewing screen Il. The tube, correction'- plate and mirror, are arranged as a unitary assembly (see particularly Figure 2) enclosed in a dust-resistant housing indicated, generally, at I8. rIhe housing VI8 is carried by a mounting standard I9, it being understood that any convenient structure may be employed to support the assembly within the cabinet. y f

In the use of such apparatus a small primary image is formed on the tube screen, which image is projected by the optical system and resolved 'Rias a magnified image on the viewing screen Il,

carried by lid I I. The correction element or plate I5 compensates for the spherical aberration introduced by mirror I4, said correction plate being positioned substantially at the center of curvature, of the mirror. The mirror and plate define an optical axis, indicated at 2U, while a pair of representative limiting rays projected from this apparatus are shown at 21-'2 I.

Since the Schmidt system is well known in optics, and since the invention is concerned with such system only insofar as it cooperates with the apparatus of the present invention, further detailed description of the sytem is not necessary herein. However, if further description of the projection television apparatus is desired, reference may be had to the above-identied disclosure of Ernest H. Traub, which includes dimensions of a representative embodiment which has proved highly satisfactory. .In `suoli a .television receiver, the cathode-ray tube screen must be properly oriented with respect to the optical axis 2U defined b y mirror I4 and correction plate I5, in order that all portions oi the projected image may focus properly upon the viewing screen I'l. Also, in the particular embodiment illustrated, the viewing screen is angled with respect to the optical axis of the Schmidt system illustrated, which would normally introduce a further out-of-focus effect.

In particular accordance with the present invention, both the general focus requirements, and correction for the out-of-focus effect introduced by the angularity of the screen, are taken care of by a novel mounting providing for ready and accurate three-dimensional adjustment of the tube screen with respect to the optical axis 2U. In the particular embodiment under consideration, the latter correction requires rotation of the tube about the center of the tube screen (as a center of rotation) in an amount equal to an angular displacement of 45l' with respect to the optical axis 2D. Such angular displacement is indicated at in Figure 1 and takes place in a plane perpendicular to the general plane of 'the viewing screen Il.

To provide for the general focus requirements aforesaid, and to make the correction necessitated-by the angularity of the viewing screen with respect to the optical'axisY 2U, the tube I3 is mounted for rotational movement about a pair ;.related directions, through a predetermined point of axes passing, in substantially right-angularly which preferably coincides with the geometrical center of the iiuore'scent screen of the tube. This point clearly appears in Figure 5, and bears the reference character 22; while the aforesaid pair 'of axes is represented at X-X and Y-Y in Figments of the tube about either the X or Y-axis willtake place about a point lying in the tube screen. y

Now making reference to Figures 2, 4 and 5, it will be observed that the neck portion 13a of the tube extends out of the housing I8 through the central aperture in correction plate I5.

Insofar as the present invention is concerned, mirror I4 and correction plate I5 may be mounted in any manner suitable to coaxially align the same. As shown, (see Figures 2 and 4) the housing I8 is provided with an annular seat 34 against which the mirror rests, said mirror being maintained in proper position by a pair of crossed resilient members 35 and 36, the ends of which are received within bayonet slots 3l. A plurality' of spring clips 3B are secured to a iiange extending inwardly around the smaller end of the housing I8, which clips serve to support the correction plate I5. The plate may be coaxially aligned with the mirror, by means of adjustable screw members shown at 39. As will be understood, the distance from the center of the mirror I4 to the center of the fluorescent screen of tube I3, (which is one of the conjugate distances of the optical system, the other being measured from the center of said mirror back to the center of the viewing screen Ill, may be adjusted by eiecting slight axial movement of the tube, under the inluence of a spring assembly presently to be described.

The tube i3 is supported by upwardly and downwardly extending bracket members 23 and 24, respectively, which members are hollow, to.

Athrough the intermediation of four arms 28 extending iorwardly to the plane containing the fluorescent screen. The usual focusing and dcflecting coils, shown at 2l and 28, respectively, surround the neck of the tube, and support of the tube within the housing may most conveniently be provided (as shown) 4by securing brackets 23 and 24 to one of the coil housings, in this instance housing 2l. As best appears in Figure 5, the coil housing 2l includes an inner cylindrical wall 29 of such diameter as to rmly support the tube I3 with freedom for axial movements (that is, movements along the Z-axis) under the influence of a spring and nut assembly 30, reacting between said coil housing and a collar 3| fixedly secured to the outermost portion of the tube. In accordance with known practice, movable quadrants 32 and 33 project outwardly beyond the coil housings and are adapted to eifect centering of the raster upon the fluorescent screen. V

As brought out supra, the arms 26 are each releasably secured to the housing i8, to accommodate rocking movements of the frame 25 about the X and X axes, selectively. This construction will be most clearly understood yby reference to Figures 2 and 5 of the drawings, it being borne in mind that pivotation of one pair of arms about one of the axes, requires sliding movement of the oppositely disposed pair of arms with respect to the points'dening the other axis. Each of the arms is ,provided with a pivot assembly adapted to secure it to the housing structure in the general plane of the iiuorescent screen of the tube I3. Upper and lower assemblies 40 and 4|, respectively, provide such pivotal securement for the vertically spaced pair of arms 26 and define the rotational axis Y-Y (Figure 3). iSimilarly, the laterally spaced pair of arms is secured to the housing by means of pivot assemblies 42 and 43. Since pivot assembly 40 is of the same construction as assembly 42, and since pivot assembly y4| is a counterpartof assembly 43, detailed description will be confined to the vertically arranged pair which denes the Y-axis, i. e., assemblies 40 and 4|. f

As is shown in Figure 2, each of the arms 26 is provided with a slotted portion 44 through grr-which passes a securing stud and an externally threaded sleeve. In the upper pivot assembly 40 (Figure 5) the stud is represented at 45 and the sleeve at 46. The assemblies 40 and 4| differ in only one respect (assembly 46 including an adjusting device not present in assembly 4|) and, accordingly, the reference characters applied to the upper assembly 40 are also applied to the pivot structure 4|, with the addition, in each instance, of the subscript a, and a single description will suiiice.

Sleeve 46 has a block portion formed integrally the arm 26 with respect to the rectangular block.

Above the plane of the arms 26 each of the assemblies 40 and 4| is provided with a knurled nut (see 48 and 48a) by means of which the slotted end of arm 26 may be drawn up tightly against the upper surface of block 41. A wing nut 49 is in threaded engagement with the upper end of stud 45 and, as will be apparent from reference to the assembly 40 (Figure 5), tightening of the wing nut serves to bring the under surface of block 41 into tight engagement with the adjacent upper surface of the housing I8.

The purpose of each of the four pivot assemblies 40, 4|, 42 and 43 is to provide for two different types of movement of the arms 26 and, therefore, rotation of the tube-carrying frame 25, about either of the twoaxes. Under one condition, the arms may be rotated about one axis while'under the other condition, each of vthe arms may be slid with respect to its associated pivot assembly, for a distance no greater than the length of the slot 44. For example, if the frame 25 is rocked downwardly about the X-axis, (as viewed in Fig- .ures 2 and 5), the lower frame support arm must slide forwardly along the block 41a of pivot assembly 4l. Similarly, during such movement of the frame, the upper arm must slide rearwardly sembly 42, Vernier adjusting devices the upper of' which is designated at 50. A spring 5| is arranged between an upwardly extending flange 52 (projecting through the slot 44 and secured to block 41) and a similar flange 53 carried by the arm 26 and positioned in confronting relation with respect to the flange 52. A screw 54 passes through spring 5| and is in threaded engagement with flange 52. As will be understood from Figthe Y-aXis. y Operation of the apparatus may be clearly ures 2 and 5, rotation of the screw 54 results in sliding movement of the upper and lower arms with respect to the sleeves 46 and 46a, and causes the frame to rotate about the X-axis. The lateral Vernier adjusting device is exactly similar to the device 50, just described, and when manipulated causes the frame and tube to rotate about understood from what follows, reference being made particularly to Figures 2, 3 and 5.

First, the tube screen is brought up to the plane of crossed axes X-X and Y-Y, by suitable manipulation of the axial adjusting device `3|), which adjustment effects movement of the tube along the Z-axis shown in Figure 3. This position of the tube screen coincides closely with proper focus of the center of the image appearing on viewing screen |1 and the image on said screen |1 is observed during the making of the adjustment. When this position has been reached, all rotative movements of the tube take place about the geometrical center of the tube screen.

When the tube has thus been properly located, axially, the general focus requirements must be met, that is, the upper and lower edges and the right and left edges of the image must be brought into sharp focus upon the viewing screen l1. Considering first the adjustment of the tube necessary to bring the right and left edge portions.

into focus, the operator prepares to rotate the frame 25-and therefore the tube |3-aboutrthel" Y-aXs; by tightening the knuried nuts strand 48a. Such tightening movement prevents sliding of the arms 26 with respect to the pivot assemblieslw and 4|, and a slight loosening of the wing nuts `49 and 49a permits the blocks 41 vand 41a to rotate with respect to the adjacent surface of housing I8. Along with these preliminary adjustments of the assemblies 40 and 4|, the knurled nuts associated with assemblies 42 and 43 are loosened, thereby making it possible for the laterally spaced pair of arms to slide with respect to their lassociated pivot assemblies 42 and 43. The screw 55, associated with lateral pivot assembly 42, is then rotated and the frame member 25 is swung about the Y-axis until the right and left hand portions of the image appear in proper focus upon the viewing screen |1.

To accomplish proper focusing of the upper and lower edges of the image, on the other hand,

l 7 frame 25 is rotated about the X-axis, defined by pivot assemblies 42 and 113, during which movement the upper and lower pair of arms are slid with respect to their` cooperating pivot assemblies 4U and 4 l. During such rotation about the X-axis the knurled adjusting nut 5d is utilized. As will be evident without further description, during this second focusing movement the knurled and wing nuts are so adjusted as to permit sliding movement of the upper and lower frame-support arms, and purely rotative movement of the laterally spaced arms.

After the above operations have been completed, the tube may be ,ret/rimmed, axially, (moved along the Z-axis), if such appears necessary to achieve the best possible focus of the center portion of the image.

Thediagrammatic showings of Figure 8 serve to further clarify the manner in which the above adjustments are effected, it being understood that pivotation of the frame 25 is shown as having occurred about the X-axis. knurled nuts associated with assemblies i2 and 43 (said assemblies being omitted from the ngure in the interest of clarity) .have .been tightened to prevent translational movement of the arms 26 with relation to said pivot assemblies, and the Wing nuts have been loosened to permit rOtation about the X-axis. Also, the knurled nuts associated with vertical assemblies have been loosened, and the frame 25 rotated downwardly thereby displacing the Y-axis to the position shown at Y-Y. Such movement of the frame N will be seen to have carried the tube i3 from the position shown in heavy lines to the position represented by th'e light outline designation. It will be appreciated that this process may be repeated in a plane 90 removed from that of the movement just described, under which conditions rotation of the frame takes place about the Y-axis.

Correction for the aforementioned out-o-focus effect (see angle created by the angularity of the viewing screen Vl with respect to the optical axis 2D is, of course, taken care of during the above-described pivotation about the X-axis, since the screen angularity is such as to cause this out-of-focus effect to appear in the upper and lower edge portions of the projected image.

It will be recognized that rotational movement of one pair of frame-supporting arms results in bodily movement, of the arms of the opposite pair, out of the planes-which they formerly occupied, and since the opposite end portions of each arm are fixed (either by attachment to the frame 25 or bythe pressure of the knurled nut 138) some bending occurs in the arms so displaced. VThis bending could take place uniformly along the arm, but in accordance with a' feature Yof this invention, freedom for such bending is provided without loss ofthe rigidity necessary in theQfra'me assembly.

As best appears in Figures 2 and 5, the arm channel-flanges 28a are each cut-away, as shown at 56 and 51, and slight bending occurs at these points in each arm when it is moved translationally with respect to its associated pivot assembly.

From the foregoing description it is evident that the present invention provides adjustable mounting. structure by means of which a cathode-ray tube, or other device having a primary image surface, may be given precise, three-dimensional orientation with respect to an optical axis. Further, the apparatus is of such a charagter that all of the focusing adjustments may be made without the necessity of gaining access t0 the housing In this instance, the

8 i8 and, since the rotational axes are individually defined, the apparatus is extremely stable during such focus adjustments.

FI claim:

z Y -1. For television apparatus and the like including a primary image screen, mechanism for angularly adjusting said screen about a predetermined point as a center of pivotation whereby 4properly to orient said screen with respect to an optical axis, said point lying substantially in said screen, said mechanism comprising, means providing a pair of individual rotational axes passing through said point in substantially right-angularly related directions and about which said screen may be adjusted selectively.

2. For television apparatus and the like including a cathode-ray tube having a face portion provided vvith an image screen, mechanism for angularly adjusting said tube about a predetermined point as a center of rotation whereby properly to orient said screen with respect to an optical axis, said point lying approximately in said vscreen, said mechanism comprising, means providing a pair of individual rotational axes passing through said point in substantially right-angularly related directions in general parallelism with the tube face and about which said tube may be adjusted selectively.

3. For television apparatus and the like including a cathode-ray tube having an image screen, mechanism for angularly adjusting said tube about a. predetermined point as a center of rotation whereby properly to orient said screen with respect to an optical axis, said point lying approximately in said screen, said mechanism comprising: a movable frame member carrying said tube and being mounted for rotation about a pair of individual rotational axes passing through said point in substantially right-angularly related dirctions, and means for effecting rotation of said frame-and consequent adjustment of said tubeabout said axes selectively.

4'. For television apparatus and the like including a cathode-ray tube having an image screen, mechanism for angularly adjusting said tube about a predetermined point as a center of rotation whereby properly to orient said screen with' respect to an optical axis, said point lying t approximately in said screen, said mechanism comprising: a movable frame member'carrying said tube and being mounted for rotation about a pair of individual rotational axes passing through said point in substantially right-angularly related directions, and means normally restraining said frame against rotation about either axis and being adjustably releasable toA provide for rotation of the frame-and consequent adjustment of said tube.-about either axis selectively.

V5.` For television apparatus and the like includ- '.ing a cathode-ray tube having an image screen,

and'

2,424,513 9, 10 means effective to lproduce rotation about the cluding a cathode-ray tube having an image axis selected. i screen, mechanism for angularly adjusting said 6. For television apparatus and the like includtube about a predetermined point as a center ing a cathode-ray tube having an image screen, o iftrotatlon whereby properly to orient said screen mechanism for angularly adjusting said tube with respect to an optical axis, said point lying about apredetermined point as a center of rota-. "'approximately in said screen, said mechanism tion whereby properly to orient said screen with comprising: a housing substantially enclosing said respect to an optical axis, said point lying aptube,a frame movably supporting theA tube Withproximately in said Screen, said mechanism coni-v in said housing, said frame being pivotally mountprising: fixed structure, a movable frame inem-i ed upon and exteriorly ofsaid housing with'freeber carrying said tube and being mounted for 'dom forV rotation about a pair of individual rotarotation about a pair of individual rotational tional axes passing through said point in Ysubaxes passing through said point in substantially stantially right-angularly related directionsy right-angularly related directions, and means means normally restraining said frame against reacting between said frame and said structure rotation about either axis, said restraining means and adjustable to eiect rotation about either of being in a position readily accessible from the eX- said axes. f terior of the housing and being adjustably releas- 7, Fonftelevison apparatus and the like inable t0 permit rotation 0f the frame abOllt either cluding a, cathode-ray tube having an image aXiS SelectiVeiy, and Control means readily a/C- screen, mechanism for angularly adjusting said Cessibie frOIn the eXteiOl 0f the housing and p0- tube about a predetermined point as a center of SitiOned t0 react betWeen said frame and housrotation whereby properly to orient said screen ing, Said COntTOl means being adjustable t0 efwith respect to an optical axis, said point lying feet rotation of the frame-and consequent adapproximately in said screen, said mechanism justment of said tube-about either axis seleccomprising: xed structure, a movable frame tivelymember carrying said tube and being mounted 11. In combination With a cathode-ray tube for rotation about a pair of individual rotational having an image Screen, a housing, apparatus axes passing through said point in substantially Supporting said tube Within Said housing With right-angularly related directions, means norfreedbm fOl angular movements about a Pair Of mally restraining said frame against rotation rotational aXeS passing thfOugh the mid-Peint 0f about either axis and being adjustabiy relaasthe screen in substantially right-angularly related able to provide for rotation of the frame .and directions and in the general plane of the screen, consequent adjustment of said tube-about either and 'adjustable means disposed eXteI'OIly 0f Said axis selectively, and means reacting between said housing and Cooperative With Said apparatus t0 trame and said structure and adjustable to eiect eftftct angular movement 0f Said tube about either rotation about the axis selected. axis.

8. For television apparatus and tli'e like in- 12 In Cotnbmatlon Wliih a Cathode-ray tube cluding a cathode-ray tube having an image having an image screen, a housing, apparatus screen, mechanism for angularly adjusting said supporting Said tube Within said hOusing With tube about a predetermined point as a center of 40 freedom for angular movements about a pail 0f rotation whereby properly to orient said screen rotational axes passing through the mid-POint with respect to an optical axis, said point lying 0f the SCreen in Substantially Tight-angularly reapproximately in said screen, said mechanism lated dlectioils and in the general plane 0f the comprising: a iiousing substantially enclosing Screen and means normally restraining Said tube said tube, a frame movably supporting the tube against rotation about either axis, said means bewithin said housing, said frame being pivotally mg disposed eXteTiOTiY 0f the hOusing and being mounted upon said housing with freedom for adiustabiy reieasabie t0 PrOvde fOr angular rotation about a pair of individual rotational movement 0f the tube about either axis seaxes passing through said point in substantially lectlvelyrightgangularly related directions, and means 13- n cOliflbiflatiOn With a cathode-ray tube reacting between said frame and said -housing having an image screen, a housing, apparatus and adiustabie to errent rotation of said frame- Supporting said tube Within said housing with and consequent adjustment of said tubeabout 'freedom fol angular movements about a pail veither axis Seiective1y of rotational axes passing through the mld-point 9. For television apparatus and the like in- 0f the Screen in Substantially right-angularly rey cluding a cathode-ray tube having an image lated dileCtiOnS and in the general planeet-the screen, mechanism for angularly adjustinglsaid Screen, means DOTmaHY restraining saidtube' tube about a predetermined pointas a center of against IOtatiOn abOut either aXiS, Said means rotation whereby properly to orient said screen being dispOsed eXteriOrly Of the housing and bewith respect t0 an optical axis, said point lying 60 ngadjustably releasable t0 provide for angular approximately in Said screen, Said mechnsm .'mOVment Of the tube about either aXiS SeleCtiVecomprising: a housing substantially enclosing 1y, land tube adjustment means disposed exteriorly said tube, a frame movably supporting the tube of said housing and effective to produce .angular within said housing, said frame being pivotally movement about the axis selected.

mounted upon and exteriorly of said housing 14.111 combination with a cathode-ray tube with freedom for rotation about a pair of indihaving an image screen, a housing, a frame supvidual rotational axes passing through' said point petting said tube with the major portion of the in substantially right-angularly related directions, latter disposed Within and enclosed by the housand control means disposed exteriorly of said ing, and means for angularly adjusting said tube housing and positioned to react between said about a predetermined point lying substantially in frame and housing, said control means being adthe screen, said means including: apparatus` pivjustable to effect rotation of said frame-and conotally supporting said frame upon said housing sequent adjustment of said tube-about, either with freedom for rotational movements about axis selectively. l said point, and control means disposed exteriorly 10. For television apparatus and the like inf of said housing and adapted to eiect rotation of '11 said frame-and consequent angular adjustment of said tubeabout said point. l

15. In combination with a cathode-ray tube having an image screen, a housing, a frame suD- porting said tube with the major portion of the latter disposed Within and enclosed by the housv 10 semblies.

means for coupling said frame to said pivot structures individually whereby to provide for angular adjustment of said tube about either axis selectively, `and a connection providing for transf "lational movement of a portion of said frame in the region of and with respect to the pivot structure not so coupled, said frame having flexibility permitting such translational movement during angular movement about either of said pivot as- INGO L. STEPHAN. 

